1. Field of the Invention
The present invention relates to a valve timing control device to be used for controlling the opening/closing timing of an intake valve or an exhaust valve in a valve actuating mechanism of an internal combustion engine.
2. Description of the Related Art
In Unexamined Published Japanese Patent Application No. 1-92504 or Unexamined Published Japanese Utility Model Application No. 2-50105, for example, there is disclosed a valve timing control device of that kind, comprising: a rotation transmitting member so mounted around a valve opening/closing rotary shaft (including a cam shaft and an internal rotor integrally mounted on the cam shaft) rotatably assembled with the head of an internal combustion engine so as to rotate relative thereto within a predetermined range for transmitting a rotating power from a crank pulley; vanes provided on the rotary shaft; a fluid chamber formed between the rotary shaft and the rotation transmitting member and halved into advancing chambers and delaying chambers by the vanes; first fluid passages for feeding and discharging a fluid to and from the advancing chambers; second fluid passages for feeding and discharging the fluid to and from the delaying chambers; a refuge hole formed in the rotation transmitting member and accommodating therein a lock pin spring-biased toward the rotary shaft; a fitting hole formed in the rotary shaft for fitting therein the head portion of the lock pin when the rotary shaft and the rotation transmitting member are synchronized in predetermined relative phases; and a third passage for feeding and discharging the fluid to and from the fitting hole.
The valve timing control device, as described in each of the above-cited patent applications is constructed such that the lock pin is moved against the spring-urging force by the fluid fed to the fitting hole via the third fluid passage. Imagining the case in which the fluid fed to the fitting hole partially leaks through the clearance between the refuge hole and the lock pin to the back pressure chamber accommodating a spring for urging the lock pin, therefore, the back pressure chamber is vented to the atmosphere so that the fluid may be discharged therefrom.
Here, the fluid to be used in the device is a working oil. When the rotating power from the crank pulley is transmitted through a timing chain to the rotation transmitting member, the working oil to be discharged from the back pressure chamber can be employed as the oil for lubricating the timing chain. When the rotating power is transmitted through a timing belt made of a resin or rubber, the working oil may cause a slipping engagement between the timing belt and the rotation transmitting member or may deteriorate the timing belt.
In order to solve these problems, we have proposed a device capable of discharging the working oil properly from the back pressure chamber, as disclosed in Japanese Patent Application No. 8-202288. This device enables to avoid those problems by causing the third fluid passage to communicate with the advancing chambers or the delaying chambers (so as to use the advancing oil pressure or the delaying oil pressure as the oil pressure for releasing the lock pin) and by causing the back pressure chamber to communicate with the delaying chambers or the advancing chambers via a fourth fluid passage.
When the advancing oil pressure is employed as the releasing oil pressure in the device of Japanese Patent Application No. 8-202288, however, the discharge passage leading from the back pressure chamber through the delaying chamber to an oil reservoir is so long that a high load is required at the releasing time to start the phase transformations before the lock by the lock pin is completely released. When the delaying oil pressure is employed as the releasing oil pressure, on the other hand, the lock pin may advance into the fitting hole at the switching time from the most delayed position to the advancing state thereby to obstruct the phase transformations or to cause malfunction of the lock pin. With the construction in which the working oil is fed to the inside of the back pressure chamber, moreover, the lock pin may be finely vibrated in the axial direction to hit the outer circumference of the rotary shaft in the refuge hole by the pressure pulsations of the working oil thereby to cause the hammering.